Industrial carbon blacks can be used in vehicle tires, industrial rubber articles, paints, toners, printing inks, plastics, other inks and in many other fields. Especially in the case of use of carbon black as a pigment, an aftertreatment of the carbon black improves particular features.
An aftertreatment of the carbon black may comprise, for example, an oxidation (JP 2000248196), coverage of the surface with chemical groups (JP 09067528, DE 10242875, EP 655516 B1, JP 09124312), drying (CN 1858531), an extraction (DE 3118907, JP 2000-290529), an activation by means of temperature or reactive gases (TW 394749 B, WO 2005/028978), a CVD process (Adv. Mater. 12(3) (2000) 16-20), mixing with other powders, grinding (DE 200700373) and the like.
Carbon black can be aftertreated in a wide variety of different apparatus and by a wide variety of different methods. For example, the aftertreatment can be effected by reaction of the carbon black with a liquid, (EP 982379, JP 2000248118), a solid (EP 1134261 A2) or a gas (JP 05078110 A).
The aftertreatment can be integrated into the preparation process by virtue of reactive substances being introduced into the filters, the transport pathways (JP 2000248196) or the pelletization (U.S. Pat. No. 4,075,160).
The aftertreatment can also be effected in separate apparatus.
One method of aftertreating carbon black is the use of fluidized beds (GB 895990). The fluidized bed enables, for example, very intensive contact of the carbon black with gaseous components, can additionally be cooled or heated, is mixed intensively and can be operated either batchwise or continuously.
The generation of fluidized beds with carbon black is restricted to carbon blacks which can be fluidized readily owing to their specific properties, for example bulk density, surface area, structure or primary particle size.
Many furnace blacks, and particularly furnace blacks in the form of coarse particles, do not form stable fluidized beds. For example, they often form channels through which the carrier gas flows. Therefore, other technologies for aftertreatment are often used for furnace blacks (JP 07-258578, JP 2001-040240), including reaction in a reactor with preceding grinding (JP 2004-075985).
EP 1347018 discloses a process for preparing aftertreated carbon black wherein the carbon black is fluidized in a fluidized bed with addition of fluidizing agents and contacted with an aftertreatment agent.
Moreover, DE 3041188 discloses stirring a carbon black bed while the carbon black is treated with gases.
It is also known that the fluidization of particles can be improved by vibration (JP 03124772) or external fields (WO 2005022667).
It is known that the fluidization can be improved by adding gases with a particularly low molecular weight (WO 00/009254).
Moreover, it is known that fluidization problems can be overcome in some cases by means of pulsation of the gas stream (Wang, Chemical Engineering Science 60 (2005) 5177-5181).
Furthermore, WO 2005/028978 discloses a fluidized bed in which a gas stream is passed into the fluidized bed horizontally in order to sufficiently fluidize fine particles.
Moreover, it is known that the incorporation and operation of horizontal (in relation to the fluidization flow) high-speed nozzles can destroy agglomerates in a fluidized bed and comminute particles (McMillan, Powder Technology, 175 (2007), 133-141).
It is known that nanoparticles in the fluidized state can be coated or reacted when the fluidization of the nanoparticles having aggregate sizes in the range of 50-1000 μm has been enabled beforehand by means of external fields (WO 05/022667).
A disadvantage of the known processes is the often limited possibility of aftertreating carbon black owing to inadequate fluidization, contamination of the carbon black in the case of use of an additional fluidizing agent, the technical complexity, in particular with regard to gas-tight systems when stirrers and vibration generators are used, the restricted applicability of external fields to electrically uncharged or non-magnetic particles, and in some cases the formation of undesired granules or other compactions with stirrers.